Fiber optics are used for a great number of applications. Everything from communication and computing systems, test and measurement systems, and medical systems and devices make use of optical technology. Optical devices are becoming increasingly smaller and more fragile.
In particular, fiberoptic telecommunications are continually subject to demand for increased bandwidth. One way that bandwidth expansion has been accomplished is through dense wavelength division multiplexing (DWDM) wherein multiple separate data streams exist concurrently in a single optical fiber, with modulation of each data stream occurring on a different channel. Each data stream is modulated onto the output beam of a corresponding semiconductor transmitter laser operating at a specific channel wavelength, and the modulated outputs from the semiconductor lasers are combined onto a single fiber for transmission in their respective channels. The International Telecommunications Union (ITU) presently requires channel separations of approximately 0.4 nanometers, or about 50 GHz. This channel separation allows up to 128 channels to be carried by a single fiber within the bandwidth range of currently available fibers and fiber amplifiers. Improvements in fiber technology together with the ever-increasing demand for greater bandwidth will likely result in smaller channel separation in the future.
Transmitter lasers used in DWDM systems have typically been based on distributed feedback (DFB) lasers operating with a reference etalon associated in a feedback control loop, with the reference etalon defining the ITU wavelength grid. Statistical variation associated with the manufacture of individual DFB lasers results in a distribution of channel center wavelengths across the wavelength grid, and thus individual DFB transmitters are usable only for a single channel or a small number of adjacent channels. Continuously tunable external cavity lasers have been developed to overcome this problem.
The advent of continuously tunable telecommunication lasers has introduced additional complexity to telecommunication transmission systems. Particularly, the tuning aspects of such lasers involve multiple optical surfaces that are sensitive to contamination and degradation during use. Lack of adequate protective packaging may decrease performance and lifetimes for such lasers.
Optoelectronics packaging is one of the most difficult and costly operations in optoelectronics manufacturing. Process manufacturing demands like submicron alignment between optical elements, high-speed electrical connections, excellent heat dissipation, and high reliability become true challenges. Providing such features has resulted in optoelectronic packages that may be larger, costlier and more difficult to manufacture than electronic packages.
In the case of an optoelectronic modules, it is difficult to align the laser diode with the optical lens or fiber when constructing the package. The process of aligning these components to a laser diode and fixing it in place is known as fiber pig-tailing. Current designs use numerous parts in complex three-dimensional arrangements and generally need high degree of accuracy and automation.
Pig tailing typically involves sealing the module and leaving a feed-through aperture open through which the optical fiber is manually threaded. Alignment of the fiber into the closed package may be challenging. Once aligned, a seal is formed coaxial with the fiber and the feed-through aperture thus hermetically sealing the package. It may be desirable to provide a hermetically sealed module which does not require threading of the fiber through the feed through.
Package designs that lend themselves to automation have been proposed which generally involve using a package with an open top, level with the plane at which an optical fiber is to be aligned. A lid is then placed over the package and sealed in place by soldering. In such cases a fiber with a metallization coating is required to ensure proper sealing.